It was a fun night! Few drinks, nice food and a "B" rate movie! How did I end up here? I knew Callum should have just stayed until the end of the film. I was staying over at his place as it was easier for work in the morning, he was house sitting for his parents who were away on some business trip. His little sister was home from Uni and it was with her that he'd left me a short while ago. I get on well with Sam, she's 18, 5ft 5, black hair and slim. I'd never really thought of her as being sexually active. The second-rate movie we we're watching got a bit steamy towards the end, I noticed she was watching intently as the movie got more erotic. When it finished I think we we're both a little out of sorts and self conscious. We both chuckled at ourselves... that broke the spell.. I said I'd better go up to bed, work and all that, she wished me good night and said she was staying up for a while, "see you in the morning then." As soon as she'd wished me good night I knew what was on her mind. I set off up the stairs, got to the 3rd step and marched on the spot, hoping that she'd not notice the difference as she was moving around in the lounge, I knew I should just leave, very quietly, and retreat in good order. Yet I knew sure as pussy tastes good what was about to happen. Whilst I was struggling with my dilemma I heard a barely audible intake off breath. I was stuck now, if I moved now she would surely see my shadow cross the doorway, my heart was pounding with trepidation, though, even as it beat like a cardiac equivalent of a Keith Moon set I felt my cock stiffen in my jeans. I could hear a soft rhythmic breathing and the slight, yet unmistakable sound of a wet clitoris being stimulated by hand. I inched toward the crack in the door, again I knew I shouldn't but I leaned forward and peered through the crack, I was greeted by the sight of Sam laid out on the couch. She'd pulled her jeans to her hips and was making the best out of having not much room, her head was hanging back over the arm of the couch, I could just see how she bit her lip from time to time, My cock was throbbing by this stage, but I had jeans on and couldn't quite get at it. I watched Sam as she'd had enough of her jeans getting in the way too, she lifted her ass off the couch and roughly pushed her jeans down to her ankles. I was then I took my moment to gain entry to my engorged penis, I had one hell of and urge to take myself in hand. I unbuttoned 2 buttons, I was unbuttoning the third when my belt betrayed me, there was a metallic clang that sounded like a death knell. I was sure she must have heard it. She'd heard something, she sat bolt upright and was reaching for her jeans. I was shitting my self- what would she say if she caught me there, and what would Callum say? She stopped, ears straining, she reminded me of a rabbit scanning for danger. I held my breath and my treacherous belt.. one noise now and that was that. It seemed like a life time, but finally she laid back again, apparently satisfied she wasn't going to be disturbed. She resumed with her pleasure. My cock was now free as well, I watched her as she modulated the rhythm and pressure she was applying, she was struggling to be quite now. There was pre-cum covering the pulsing head of my stiff cock, she deftly maneuvered between clit and roughly fingering deep inside, she yanked her top up and pulled hard at her nipple, her back arched and I saw how hard she was trying to stifle the sound as a shuddering orgasm ripped through her petite frame... I exploded, I tried to catch the evidence of my indiscretion, I was betrayed again as spunk overflowed the cup I'd prepared for it's arrival. as soon as I saw my seed hot the floor I snapped back to reality. I stood outside the door with my cock out and a hand full of hot spunk... I was freaked... I heard movement, I peaked through the crack, to my sheer good fortune she turned and went through the kitchen door. I took my chance and ascended the stairs like a shadow.